I don't know about TV, but I have an old Ampeg that does this with radio signals at my rehearsal space. According to someone more knowledgeable than myself, it doesn't have to be the amp itself. Can be the cord, or even the wiring in that building. Of course it might be the amp too.
sometimes amps can pick up radio frequencies. have an amp tech look into it--maybe a resistor or capacitor tweak may help--not sure. on another thread guys that have divided by 13 amps have had the problem too. a tech mentioned how to fix it. he used a .047uf ceramic cap between the input jack ground & the chassis for each channel. he also soldered the cap to the metal of the rotary switch. this won't necessarily work for you--depends on the amp you have, but a tech may have an idea in the ballpark
Unplug the cable to the input and power it up. If you still get TV then it's in the amp. Otherwise it's a cable or a pedal doing it. I've had a pedal, I can't remember which, that would pick up RF. Mostly it's a poor cable that picks up the RF.